Method of and apparatus for completing wells



T. A. KIBBY 2,896,718

METHOD oF AND APPARATUS Foa COMPLETING WELLS July 28, 1959 Filed Aug. 3, 1955 m u m r) .....a.,.............` A... n.. n,...

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KUnited States Patent O f 2,896,718 METHOD F APPARATUS FOR COMPLETING WELLS Theodore 'A. Kibby, San Tome, Venezuela, assigner to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania I Application August 3, 1955, Serial No. 526,171 3 Claims. (Cl. 166-35) This invention relates to a method of and apparatus for completing wells, and more particularly, to a method and apparatus for producing a well structure in a producing formation which comprises a perforated tubing and a surrounding cement sheath having a system of small fractures therein. This application is a continuation-inpart of my copending patent application, Serial No. 450,- 630, led August 18, 1954, now abandoned.

The method of the invention is especially useful for completing wells in poorly consolidated formations where sand control is a problem. In producing oil, gas, or other fluids from poorly consolidated formations such as unconsolidated sands, it is desired to avoid the production of sand with the fluids in order to prevent costly shutdown, flue to clogging of the well bores, and to avoid damage to pumps and other well equipment. A number of procedures for sand control have been employed including the use of various types of strainers in the producing formation; for example, wire-wrapped slotted pipes, gravel packs, and the like. The prior art means for sand control have not been entirely satisfactory. Abrasion caused by sand particles enlarges the openings in the wirewrapped slotted pipe and allows the production of substantial quantities of sand which usually accumulates in the well bore, stopping production and necessitating an expensive clean-out process. The openings in the pipe are also subject to clogging by sand with resulting decrease in production. Gravel packs are also subject to clogging. This is due to the fact that it is diicult to place the gravel in the well without forming voids in some places in the pack. Such voids allows shifting of the gravel during production and consequent movement of sand which clogs fluid passages in the pack and stops or reduces production.

In completing wells in consolidated producing formations certain problems can occur when conventional methods of completing wells by gun perforation are practiced. Recent evidence indicates that when bullets or shaped charges from a gun or jet perforator are red through a well casing and into a consolidated producing formation, drilling mud or other solids may be forced into the perforations. When this occurs the productivity of the formation is poor. Tests show that the mud or other finely divided solids can form a solid plug in the perforation. In some instances mud is even forced into the pores of the consolidated formation and reduces permeability. The method of the present invention can avoid these problems of low productivity which can occur in wells completed in consolidated formations by gun perforation.

`The patent applications of Abraham J. Teplitz, Serial Number 424,862, filed April 22, 1954, now abandoned, and Serial Number 501,063, led April 13, 1955, describe a new method of completing wells which makes possible the production of oil from unconsolidated oil sands without the production of substantial quantities of sand and which, when applied to the completion of wells in consolidated formations, avoids the problems of mud plugging which are encountered in well completion by conventional gun perforating. In the new method a tubular casing is installed in the rwell in the-producing formation and a cement 'sheath is Vformed VaboutY the casing in the annularV space between the' casing and the 2,896,718 Patented July Y 1959 ICE.

sheath. The present invention is directed to an improved specific embodiment of the method for completing a well described in said Teplitz applications and to a novel apparatus for use in the method. l

The concept of the present invention in general comy prises installing in a well drilled in a producing formationa tubular casing coaxial with the borehole, forming a cementitious sheath in the annular space between the casing and thev walls of the producing formation, and tiring from within the casing and into the wall of said casing a bullet having a substantially conical point and an annular shoulder at the base of its point for arresting the forward movement of the bullet-after the point has pierced the wall of the tubular casing. The result of this operation is that the casing is perforated and small fractures are formed in the cement sheath which provide passsages for fluids from the producing formation into the perforations in the casing. The shoulder prevents the bullet from passing through the cement sheath and forming llarge openings in the sheath which could pass sand into the casing. Furthermore, since the bullet does not pass through the cement sheath and into the producing formation, there is no forcing of mud under high pressure into the formation.` Therefore, when the method of the invention is applied to' the completion of a well in a consolidated or competent formation, the low permeability which results from the forming of a mud cake or plug in the bullet channels in wells completed by conventional bullet perforation, is avoided in the method of my invention.

Further description of the details of the invention can best be given by referring to the drawing of which Figure 1 is a diagrammatic sectional view of a producing formation in an oil well showing a phase in the completion of the well by the method of the invention; Figure 2 is a diagrammatic sectional view of the producing Zone of an oil well completed in accordance with the method of the invention; and Figure 3 is a diagrammatic perspective view of a bullet used in the method of the invention.'

Figure 1 shows, by way of example, a well extending through a consolidated formation 10, an unconsolidated oil sand 11 and into a consolidated formation 12. The

well is cased throughout the producing formation with a tubular casing 14, which is preferably steelcasing pipe commonly used in the art. The casing 14 is surrounded by a cementitious sheath 15, formed preferably from a slurry of neat Portland cement. Care -is taken to el-iminate voids or channels from the cement sheath 15 before it sets, for example by using scratchers and centralizers in the cementing operation. After the'cement has set, the well is ready for the phase of the method of the invention in which fractures are formed in the cement sheath and perforations are formed in the tubular casing.

`In my invention, a modified gun perforating device 20 is lowered into the well to the level of the producing formation 'as shown in Figure 1. Gun perforating devices, well known in the art, areV provided with one or more gun barrels for tiring projectiles into the inner wall of a well casing. A known type of ring device may be employed, but in my invention the gun is modied in that the barrels are loaded with bullets generally of the structure indicated in Figure 3 and each having a smaller than conventional powder charge of amountvto be explained later. A basket 24 whose purpose will also become evident later may be' suspended below'V the as 3 Figure 3 shows a bullet It is conveniently Yof caliber to t a commerciallyavail` ableperforating gun barrel, and has a cylindrical body portion 25 and. coaxial with the body portion, a generali ly-pointednose portion'27. vThe nose portion may be.

- conicalorpyramidal ork other generally-pointed shape with sharp or slightly rounded point, and may have a llet at its base. The base of the nose portion 27` yis substantiallysmaller. in cross-section than the cylindrical body 25, thus forming a shoulder 28-at the junctureof the base of the nose portion and the body of the bullet.

This shoulder 28` is adapted to impede the penetration of the bullet into the well casing pipe toa depth greater than the length of the nose 27, and thereby arrest the bullety before the body portion ZS'traverses the well caswhich is used in my invention.-

f tion was conducted in a shallow test hole.

ing. The nose 27 of thebullet should have aflength somewhat. greater Vthanthe knownthickness of the casing I4. l

In my invention, bullets of the structure illustrated in- 'Figu're 3r are tired' by the modified gun device 20 against ythe yinner wall `of the well casing. When the proper propellant charge is used, thebullet pierces the casing, but

f its forward `motion isv arrested by impact of the shoulder 2S againstthe casing 14, so that the bullet'does notfpassi through the casing or the cement sheath.i In most instances, the shoulder causes the bullet to rebound from the hole in the casing wall, leaving a small tapered substantialv extent into thecement sheath, the bullets f apply a kstress which fractures the sheath and rformsy la system of hair-line fractures or cracks therein.

The well structure resulting from carrying out my invention for. completing. a well is illustratedv in Figure 2 of the drawing. As the figure shows,r they tubularcasing 14 is positioned -within the producing formation coaxial with the borehole and is surrounded by a cement sheath 15. The casing 14 in the producing formation contains perforations 18 in its walls which were. pierced by the point 27 of the bullets employed in the invention. The cement sheath 15 in the. producing formation contains a system of small fractures or fissures 22 caused by the shock of the bullet shoulder 28 striking against the tubular casing 14. The fractures are the only openings in the cement sheath; there are no large passages such as would be formed by 4a bullet passing completely through the sheath. The small fractures, which are the only openings in the sheath, pass fluids from the unconsolidated producing Iformation into the perforations in the well casing but. prevent the passage of. sand in any substantial amount. The sheath retains its original general outline as Figure 2, Shows, and continues to provide supportfor the surrounding unconsolidated sand formation so that the shifting of sand which causes clogging in wells completed in sand formations by conventional methods is avoided.

The caliber and the material of composition of bullets employed. in the pnactice of the invention can vary depending upon the wall thickness of the particular casing to be piercedand the thickness ofthe sheath to be fractured. Bullets of calibers and of materials conventionally used for perforating well casing are suitable, such as steel alloy bullets of from about 1/16 to *V16 inch in diameter. The proper propellant charge for the bullets is. substantially smaller than that normally employedfor casing perforation by conventional methods wherein bullets are tired into the producing formation after completely traversing the. casing, and its cement sheath. The reduced propellantA charge, and the effect of thev bullet shoulder 28 prevent the bullets from passing through the casing into the cement sheath. In the practice of my invention, the propellant charge should' be .from

about Mt to T/ the charge normally employed to propel l bullets ofthesame caliber in conventional casing-perfof ration operations in which the bulletk entirely traverses the casingA and' itscement sheath,V the proper charge in any particular instance being readily determinable by any one of several procedures yto be described.l

The eicacyof my invention for piercing casing and cracking a cement sheath surrounding the casing-was determinedin the following testysehup. tlnasmuch as itis. impossible to recover vthe cement sheath, the test opera- In one such test a section of 51/2 inch casing was cemented concentrically inside a 9% inch casing; After the cement had set, a 4 foot by 8 inch Vsection was cut from the side of the outer casing tok serve as a window for observing the` xresult of the invention.

The outer pipe was Ithen Wrapped with wire about the cut-away portion and the assembly waslowered into ya shallowk test-hole.- A gun y y perforating device was lowered into the inner casing and 10 shoulder bullets of they structure shown .in Figure 3 of the drawing, 0.471 inch in? ydiameterand loaded with .one-half thenormal propellant charge, were tired into the inner wall of the 51/2 inch casing. The assemblyy wasraisedfrom the hole' and examined. -It was found that the bullets had pierced the inner 51/2 inch. casing and l had .fractured the cement sheath. The 'fractures' in the the. bullets stopped when its shoulder struck the inside.

- thecasing` wall,-they impart a sharp physical shock: to

the cement sheath. Thus, without penetrating to: any

cement were ne but numerous iandi rradi-ated .outwardly from the holes punched in the inner casing. Each of of the 51/2 inch casing and most of the bullets. bounced back leaving a clear hole in the casing.

It. is important in the practice of my invention that the powder charge beproperly related to the weightand diameter of bullet, length of barrel (which is determined by theavailable hole diameter) and the type-of casing which it is desired to pierce The above-described test .procedure-may also be used to experimentally determine the proper -amount of propellant charge to tbe employed so that the bullet nose 27 will pierce the casing but the bullet will be arrested when its shoulder 28 strikes the casing. By way of example, a bullet having the shape illustrated in Figure 3, weighing 14.45 gram, having an outside diameter of 0.471 inch, and a nose 27 in the shape of a cone of base diameter 5/6 inch and height 1/2 inch, was red with reduced charge from a commercially-avaiL able 4 inch gun into a short length of 7 inch type l-55 casing (wall thickness 0.3 inch) in the above-described test set-up. The charge customarily used in this gun for conventional casing-perforating service is 10 grams, which charge is suicient to cause the bullet to entirely traverse the casing and its cement sheath. The abovedescribed bullet of my invention, fired from this 4 inch gun with only a 5 gram powder charge produced a tapered hole in the 7 inch type l-55 well casing, the hole tapering down to approximately is inch in diameter at its outer end, and the shoulder of the bullet indented the steel lessV than 1/16 inch. The proper propellant charge to cause the bullet to pierce the casing but not traverse the casing is thus readily determinable in the test set-up described above wherein the known casing string (or strings) and. the cement in the well around the casing may he duplicated.

Alternatively the proper charge may in any particular instance be determined directly in the well by reducing: the conventional charge known to be required for the bullet to entirely traverse the casing until it is found that the bullets may be recovered inside the well, for example, by means of a basket carried beneath the shooting gun as indicated generally by 24 in Figure 1 or by means of a fishing magnet (not shown). The basket 24 should be of the drillable type and may be connected to the gun 20 by means `of a shear pin 25 so that the gun may be recovered in the event that the basket gets stuck. 'Ihe basket 24 may have the conventional form of an inverted umbrella made of reinforced rubber or other drillable material and constructed so that its periphery conforms approximately to the inner surface of the casing. The proper quantity of propellant charge for use in my invention is one which is reasonably large but which allows the bullet to remain inthe well bore, rather than cause the bullet to traverse the casing and lodge in the surrounding cement sheath. In a well in any particular situation, the proper weight of charge is readily determined as the maX- imum charge which still allows the bullet to be recovered from the well bore. The bullets may be recovered in the basket 24 or by means of a junk basket or fishing magnet subsequently run into the hole. The eiiicacy of the piercement may be determined by applying liquid (preferably oil) under pressure to the well over the depth interval concerned, and if the liquid readily passes through the casing it is known that the casing has been pierced. By way of example, in one well -a number of 14.45 gram bullets 0.471 inch in diameter were tired from a 4 inch gun with 3 gram propellant charges, the bullets being afterward recovered. The depth interval was then pressure tested with oil but found not to be open. The gun was then reloaded with similar bullets but each with a 4 gram propellant charge. Subsequent to firing the bullets were again recovered, but a pressure test showed thatv there was still no communication to the formation. The gun was then again reloaded with similar bullets and each was given a 5 gram propellant charge. Subsequent to iiring the bullets were again recovered and a pressure test with oil showed that communication to the formation had this time been established. Accordingly, the 5 gram charge was indicated to be the proper charge for use in this well or others having similar well equipment.

The steps to be followed in the practice of my invention are to cement the casing through the producing formation taking care to obtain the best possible cement job and avoiding the formation of all voids in well known manner. At the same time a short length of the same casing may be cemented into a short length of larger casing to form a test set-up as previously described to duplicate well conditions at the surface. A commercially-available casingperforating gun of the conventional type is then charged with the shoulder bullets of my invention, and with several different powder charges each smaller than that conventionally used with bullets of comparable weight. After the cement in the test set-up has properly set, the bullets are fired in the test set-up and it may be found that the largest charge causes the ybullet to entirely traverse the casing, whereas the smallest charge will be insufficient to cause the bullet to even pierce the casing at all. An intermediate charge will be found which causes the bullet nose to pierce the casing but the bullet will still remain inside the casing. The largest charge which will do this is indicated and the gun may then be loaded with this charge for shooting in the well. This gun 20 and basket 24 may then be lowered into the well and the gun fired opposite the producing formation. Upon removing the gun and basket from the hole, the bullets will be found recovered in the basket 24. Alternatively to using the basket 24 on the gun, the bullets may be recovered with a magnet or a junk basket subsequently run to the bottom of the hole. As a further check yon whether the casing is pierced and the cement fractured, oil may be spotted opposite the formation and pressure applied by means gf a pump at the surface. If communication to the formation exists, the oil will move out into the formation. Subsequently, of course, the well is put on production in conventional manner.

After the well is completed in accordance with my invention, if it should appear that insufficient fractures had been developed in the cement sheath and that the cement is not permeable enough for the desired rate of production of liuids, the fractures can be made more permeable by any of a number of well known methods, for example, by treatment with an acid such as hydrochloric acid. In the event that the casing had been pierced, without fracturing the cement sheath at all, such fractures may be produced by one of the techniques described in th afore-mentioned Teplitz applications.

In the foregoing description, I have referred only to the completion of a well at a single producing level. However, it should be understood that aV well drilled through a plurality of producing formations can be completed at each level by the method of my invention so that production can take place simultaneously from each formation. This characteristic of my method is an irnportant advantage over conventional methods of well completion, such as gravel packing, which cannot be applied to widely separated producing zones in a single well.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

l. Apparatus for piercing pipe in a well comprising a gun barrel adapted to be lowered into the Well, means for tiring said gun, a bullet in said gun having a cylindrical body portion and a generally conical nose portion coaxial with the body portion, the length of said nose portion being greater than the thickness of the pipe to be pierced, the base of the conical nose being substantially smaller in diameter than the cylindrical body and thereby forming at the juncture of said nose and body an annular shoulder adapted to impede penetration of the body portion of the bullet into the pipe, an explosive charge in said gun adapted to propel said bullet from the gun with a velocity suicient to elfect piercement of the pipe by said conical nose but insuftcient to cause perforation of the pipe by the body portion of the bullet whereby said bullet remains inside the pipe, and means attached below said gun adapted to catch said bullet.

2. Apparatus adapted to punch a hole in a target which comprises a gun barrel, a bullet having a substantially cylindrical body portion and a generally pointed nose portion coaxial with said body portion, the length of said nose portion being greater than the thickness of the target, the base of said pointed nose being substantially smaller in cross-section than said body portion and thereby forming at the juncture of said nose and body a shoulder adapted to impede penetration of the body portion of the bullet into the target, and a propellant for said bullet adapted to propel said bullet from the gun barrel with a velocity sulicient to effect piercement of the target by the nose of said bullet but insucient to cause perforation of the target by the body portion of the bullet.

3. A method of completing a well in which a casing is cemented in the producing formation, comprising the steps of piercing the casing with a solid object to make an opening therethrough, and simultaneously striking the inner surface of the casing about the periphery of the opening pierced in the casing with said solid object to apply a sharp physical shock to the casing suiiicient to fracture the cement surrounding the pierced portion of the casing to `form small cracks in the cement communicating between the producing formation and the opening pierced in the casing.

References Cited in the file of this patent UNITED STATES PATENTS 2,029,491 Lane Feb. 4, 1936 2,157,729 Church May 3, 1939 2,191,750 -Brown Feb. 27, 1940 2,381,929 Schlumberger Aug. 14, 1945 2,400,878 Dunn ,May 28, 1946 

